I am always present when she has sex with anyone other than me. We're a couple, shes not single. We only play together. For her comfort and safety I am always present. Its not something we bend on. It was something we agreed upon prior to involving others in our bed. Not every couple will be like us, but if you plan on being a bull you need to be comfortable with the fact your boning a married woman.
Consider this carefully, would you rather a husband be present, consenting and know hes ok with you sexing his wife or woukd you rather take the risk on a cheating wife unsure how her husband woukd react if he discovered the affair? With cheating wives and never meeting the husband, you are taking worse risks.